Method and device for combustion of solid fuel

ABSTRACT

The invention relates to a method and device for converting energy by combustion of solid fuel, especially incineration of bio-organic fuels and municipal solid waste to produce heat energy and which operates with very low levels of NO x , CO and fly ash, in which that the oxygen flow in the first and second combustion chambers are strictly controlled by regulating the flow of fresh air separately into each combustion chamber in it least one separate zone and by scaling off the entire combustion chambers in order to eliminate penetration of false air into the chambers, the temperatures in the first and second combustion chamber are strictly controlled, in addition to the regulation of the oxygen flow, by admixing a regulated amount of recycled flue gas with the fresh air which is being led into each of the chambers in each of the at least one separate zones, and both the recycled flue gas and fresh combustion gases are filtered in unburned solid waste in the first combustion chamber by sending the unburned solid waste and the gases in a counter-flow before entering the gases into the second combustion chamber.

[0001] This invention relates to a method and device for convertingenergy by combustion of solid fuel, especially incineration ofbio-organic fuels and municipal solid waste to produce heat energy andwhich operates with very low levels of NO_(x), CO and fly ash.

BACKGROUND

[0002] The industrialised way of living produces enormous amounts ofsolid municipal waste and other forms of solid waste such as forinstance rubber tyres, construction materials etc. The vast amounts ofthese solid wastes have in many highly populated areas grown into amajor pollution problem simply due to its volume which has consumedmajor parts of the available deposition capacity in the area. Inaddition, there are often strong restrictions to deposition places sincemajor parts of this waste is only slowly biodegradable and do oftencontain toxic substances.

[0003] One very effective way of reducing the volume and weight of solidmunicipal waste, and which also may destroy many toxic substances, is toburn it in incinerators. This may reduce the volume of uncompacted wasteup to 90% leaving an inert residue ash, glass, metal and other solidmaterials called bottom ash which may be deposited in a landfill. If thecombustion process is carefully controlled, the combustible part of thewaste will be transformed to mostly CO₂, H₂O and heat.

[0004] Municipal waste is a mixture of many different materials with awide variety of combustion properties. Thus, in practice there willalways be some degree of incomplete combustion involved in solid wasteincinerators which produce gaseous by-products such as for instance COand finely divided particulate material called fly ash. Fly ash includescinders, dust and soot. In addition there are also difficulties incontrolling the temperature in the incinerator so carefully that one hasa sufficiently high temperature to achieve an acceptable degree ofcombustion of the waste, but low enough to avoid the formation ofNO_(x).

[0005] In order to avoiding these compounds from reaching theatmosphere, modern incinerators must be equipped with extensiveemission-control devices including fabric baghose filters, acid gasscrubbers, electrostatic precipitators etc. These emission-controldevices introduces substantial additional costs to the process, and asresult, waste incinerators with state of the art emission control arenormally up-scaled to capacities of delivering 30-300 MW of heat energyin form of hot water or steam. Such enormous plants require very largeamounts of municipal waste (or other fuels) and do also often includevery extensive pipelines to deliver the heat energy to numerouscustomers spread over a wide area. Thus this solution is only suited formajor cities and other large heavily populated areas.

[0006] For smaller plants, there has presently not been possible toobtain the same degree of emission-control due to the investment andoperation costs of the emission-control devices. Presently, this hasresulted in more generous emission permits for smaller wasteincineration plants which produce less than 30 MW of heat energy and canthus be employed in smaller cities and populated areas.

[0007] This is obviously not an environmentally satisfactory solution.The constantly increasing population and energy consumption of themodern society exerts a growing pollution pressure on the environment.One of the most immediate pollution problems in heavy populated areas isthe air quality. Due to extensive use of motorised traffic, heating bywood and fossil fuels, industry, etc. the air in heavy populated areasare often locally polluted by small particles of partly or fullyunburned carcinogenic remains of fuels such as soot, PAH; acid gasessuch as NO_(x), SO₂; toxic compounds such as CO, dioxin, ozone, etc. Onehas recently become aware of that this type of air pollution has a muchlarger impact on human health than previously assumed, and leads to manycommon diseases including cancer, auto-immune diseases and respiratorydiseases. The latest estimates for Oslo city, population approx. 500000,is that 400 people die each year due to diseases that can be traced tobad air quality, and the frequency of for instance asthma issignificantly larger in heavily than in scarcely populated areas. As aresult of this knowledge, there are being raised demands for decreasingthe emission permits of the above mentioned compounds.

[0008] Thus there is a need for waste incinerators that can operate onsmaller waste volumes produced by smaller communities and populatedareas with the same level of emission-control as the larger incinerators(>30 MW) with full cleansing capacity, and without increasing the priceof heat energy. Typical sizes of the smaller plants are in the range of250 kW to 5 MW

[0009] Prior Technology

[0010] Most incinerators employs two combustion chambers, a primarycombustion chamber where moisture is driven off and the waste is ignitedand volatilised, and a second combustion chamber where the remainingunburned gases and particulates are oxidised, eliminating odours andreducing the amount of fly ash in the exhaust. In order to provideenough oxygen for both primary and secondary combustion chambers, air isoften supplied and mixed with the burning refuse through openingsbeneath the grates and/or is admitted to the area from above. There areknown solutions where the air stream is maintained by natural draft inchimneys and by mechanical forced-draft fans.

[0011] It is well known that the temperature conditions in thecombustion zone is the prime factor governing the combustion process. Itis vital to obtain a stable and even temperature in the whole combustionzone at a sufficient high level. If the temperature becomes too low, thecombustion of the waste will slow down and the degree of incompletecombustion will rise which again increases the levels of unburnedremains (CO, PAH, VOC, soot, dioxin etc.) in the exhaust gases, while atoo high temperature will increase the amount of NO_(x). Thus thetemperature in the combustion zone should be kept at an even and stabletemperature of just below 1200° C.

[0012] Despite numerous extensive trials of achieving good control ofthe air flow in the combustion zones, state of the art incinerators dostill produce sufficiently high levels of fly ash and the other abovementioned pollutants that the exhaust must be subject to extensivecleansing by several types of emission-control devices in order to reachenvironmentally acceptable levels. In addition, most conventionalincinerators must also employ expensive pre-treatments of the waste fuelin order to upgrade the fuel and thereby reduce the formation of forinstance fly ash.

OBJECT OF INVENTION

[0013] The main object of this invention is to provide an energyconverter plant for solid waste which operates well below the emissionregulations valid for incinerators larger than 30 MW with use of onlymoderate emission-control devices at the exhaust outlet.

[0014] It is also an object of this invention to provide an energyconverter plant for solid municipial waste which operates in acontinuous process on a small scale, in the range of 250 kW to 5 MW andwhich can produce heat energy in form of hot water and/or steam at thesame price level as large incinerators above 30 MW.

[0015] A further object of this invention to provide an energy converterplant for solid waste which can operate on small scale in the range of250 kW to 5 MW and employ all kinds of solid municipal waste, rubberwaste, paper waste etc. with water contents up to about 60%, and whichcan operate with very simple and cheap pre-treatment of the fuel.

SHORT DESCRIPTIONS OF THE DRAWINGS

[0016]FIG. 1 shows a preferred embodiment of an incineration plantaccording to the invention seen in perspective from above.

[0017]FIG. 2 shows a schematic diagram of the incineration plant shownin FIG. 1.

[0018]FIG. 3 shows an enlarged drawing of the primary combustion chamberof the incineration plant shown in FIG. 1.

[0019]FIG. 3 shows an enlarged drawing of the primary combustionchamber.

[0020]FIG. 4 shows an enlarged side view of the lower part of theprimary combustion chamber seen from direction A in FIG. 3.

[0021]FIG. 5 shows an enlarged side view of the lower part of theprimary combustion chamber seen from direction B in FIG. 3.

[0022]FIG. 6 shows an enlarged cross-section of the inclined side wallmarked as box C in FIG. 4. The cross-section is seen from direction Aand shows an enlarged view of the inlets for air and flue gas.

[0023]FIG. 7 is a side view of the secondary combustion chamberaccording to a preferred embodiment of the invention intended for fuelwith low heat values.

[0024]FIG. 8 is an exploded view showing the internal parts of thesecondary combustion chamber shown in FIG. 7.

[0025]FIG. 9 shows a side view of a second preferred embodiment of thesecondary combustion chamber intended for fuels with high heat values.

BRIEF DESCRIPTIONS OF THE INVENTION

[0026] The aims of the invention can be achieved by an energy convertingplant according to the following description and appended claims.

[0027] The aim of the invention can be achieved by an energy converterfor instance an incinerator plant for solid fuels which operatesaccording to the following principles:

[0028] 1) ensuring a good control of the oxygen flow in the combustionchamber by regulating the flow of fresh air which is led into thechamber in at least one separate zone and by sealing off the entirecombustion chamber in order to eliminate penetration of false air intothe chamber,

[0029] 2) ensuring a good control of the temperature in the combustionchamber by admixing a regulated amount of recycled flue gas with thefresh air which is being led into the chamber in each of the at leastone separate zones, and

[0030] 3) filtering both the recycled flue gas and fresh combustiongases in unburned solid waste in the first combustion chamber by sendingthe unburned solid waste and the gases in a counter-flow before enteringthe gases into the second combustion chamber.

[0031] The combustion rate and temperature conditions in the combustionchamber are largely controlled by the flow of oxygen inside the chamber.It is therefore vital to achieve an excellent control of the injectionrate, or air flow velocity of the fresh air which is led into thecombustion chamber for all injection points. It is also an advantage tobe able to regulate the injection points independently of each other inorder to meet local fluctuations in the combustion process. It isequally vital to avoid false air penetration into the chamber sincefalse air gives an uncontrolled contribution to the combustion process,and will normally lead to a less complete combustion and thereby anenhancement of pollutants in the flue gases. The penetration of falseair is a common and serious problem in prior art. In this invention thecontrol with false air is solved by sealing off the entire combustionchamber against the surrounding atmosphere and sluicing solid waste intothe upper part of the combustion chamber and bottom ash out of thebottom part of the combustion chamber.

[0032] In conventional incinerators it is often found that when thecontent of CO is low in the flue gas, the content of NO_(x) is high andvice versa, when the content of NO_(x) is low the content of CO is high.This reflects the difficulties encountered in regulating thetemperatures of the combustion zones in conventional incinerators. Asmentioned, too low combustion temperatures leads to a lesser degree ofcomplete combustion and larger CO contents in the flue gases, while toohigh combustion temperatures leads to production of NO_(x). Thus whenthe temperature is controlled by just regulating the amount of oxygen(air) entering the combustion zone, it has proven difficult to obtain anadequate and simultaneous temperature control of both the areas adjacentto the oxygen inlets and in the bulk combustion zone. That is, it isdifficult to obtain both a sufficient low temperature in the areaadjacent to the inlets to avoid NO_(x)-formation and a sufficient hightemperature (i.e. combustion rate) in the bulk areas to avoidCO-formation. In prior art, the temperature of the inlet areas will inpractise be too high if the temperature of the bulk area is adequate,and if the temperature of the inlet areas is adequate the temperature ofthe bulk area becomes to low. This problem is solved by the presentinvention by admixture of recycled inert flue gas which functionspartially as a chilling fluid and partially as a thinner which reducesthe oxygen concentration in the combustion chamber. Thus it becomespossible to maintain a sufficiently high supply-rate of oxygen tomaintain a sufficiently high temperature in the bulk area withoutoverheating the inlet zones. This gives another advantage since theadmixture of recycled flue gas and fresh air in the combustion zonesmake it possible to maintain a rapid over-all combustion rate, i.e.large incineration capacity without danger of over-heating of thecombustion zone.

[0033] A common problem of incinerators is that the air flow inside thecombustion chamber is often sufficiently rapid to entrain and carryalong large quantities of particulate matter such as fly ash and dust.This leads, as mentioned, to an unacceptable high content of fly ash anddust in the gas flow in the entire incineration plant and makes itnecessary to install extensive cleansing equipment on the exhaustoutlet. The problem with fly ash can be considerably reduced/eliminatedby filtering the flue and unburned combustion gases in the firstcombustion zone by sending them in a counter-flow through at least aportion of the unburned solid waste inside the primary combustionchamber. This removes a large portion of the fly ash and other solidparticles entrained in the gas leaving the first combustion chamber, andthus from all subsequent combustion chambers of the incinerator plant,and will therefore reduce/eliminate much of the need for cleansing ofthe exhaust gases. This constitutes a very efficient and cheap solutionof the problem with fly ash and other solid particulate materials in theexhaust from incinerators.

[0034] Another advantage is that since most of the fly ash is retainedin the primary chamber, the plant can operate with less strict demandsfor pre-treatment of the solid waste. Prior art incinerators have oftenmet the problem of fly ash by efforts to produce less fly ash bypre-treating and/or up-grading the waste by for instance sorting,chemical treatments, adding hydrocarbon fuels, pelletising, etc. Forincinerators according to the invention, all these measures are nolonger needed. Thus the handling of the solid waste can be made verysimple and cost effective. A preferred way is to pack or bale the wasteinto large lumps which are wrapped in a plastic foil such as apolyethylene (PE) foil. This gives easy to handle and odourless baleswhich are easy to sluice into the combustion chamber.

DETAILED DESCRIPTION OF THE INVENTION

[0035] The invention will now be described in more detail with referenceto the accompanying drawings which shows a preferred embodiment of theinvention.

[0036] As can be seen from FIGS. 1 and 2, the preferred embodiment of anincinerator plant according to the invention comprises a primarycombustion chamber 1, a secondary combustion chamber 30 with a cyclone(not shown), a boiler 40, a filter 40, a pipe system for recycling andtransportation of flue gas, pipe system for supplying fresh air, andmeans for transporting and inserting the bales of compacted solid waste80.

[0037] Primary Combustion Chamber.

[0038] The main body of the primary combustion chamber 1 (see FIGS. 1-3)is shaped as a vertical shaft with a rectangular cross-section. Theshaft is given slightly increasing, dimensions in downward direction inorder to avoid jamming of the fuel. The upper part of the shaftconstitutes an air tight and fireproof sluice 2 for insertion of thefuel in form of bales 80 of solid municipal waste, and is formed bydividing off a section 5 of the upper part of the shaft by inserting aremovable hatch 7. The section 5 will thus form an upper sluice chamberconfined by the side walls, the top hatch 6 and bottom hatch 7. Thesluice chamber 5 is equipped with an inlet 3 and outlet 4 for recycledflue gas. In addition there are a side hatch 8 which acts as a safetyoutlet in case of unintended violently uncontrolled as generations orexplosions in the combustion chamber. The recycled flue gas entering theinlet 3 is taken from the exhaust pipe 50 and transported by pipe 51(see FIG. 2). The pipe 51 is equipped with a valve 52. The outlet 4 isconnected to a by-pass pipe 54 which directs the gas to a junction 66where it is mixed with recycled flue as and fresh air to be injectedinto the primary combustion chamber. The functioning of the fuel sluice5 can be described as follows: First the bottom hatch 7 and valves 52and 53 are closed. Then the top hatch 6 is opened and a bale 80 of solidwaste wrapped in PE-foil is lowered through the top hatch opening. Thebale has a slightly less cross-sectional area than the shaft (in boththe sluice chamber 5 and combustion chamber 1). After the bale 80 hasbeen placed into the sluice chamber 5, the top hatch 6 is closed andvalves 52 and 53 are opened (bottom hatch 7 is still closed). Thenrecycled flue gas will flow into the empty space in the sluice chamberand ventilate out the fresh air that entered the chamber duringinsertion of the fuel bale 80. Finally, the bottom hatch 7 is opened tolet the fuel bale slide downwards into the combustion chamber 1 and theoutlet valve 53 is closed such that the recycled flue gas enteringthrough inlet 52 is directed downward into the combustion chamber. Thebottom hatch 7 will continuously try to close the opening, but isequipped with pressure sensors (not shown) that will immediately feelthe presence of a waste bale in the opening and retrieve the bottomhatch 7 to the open position. Thus, once the fuel bale has slid to alevel just beneath the bottom hatch 7, the bottom hatch will be closedand the sluice process can be repeated. In this way, the fuel is neatlyand gently sluiced into the combustion chamber with very littledisturbance of the combustion process since the combustion chamber 1 isat any time filled with a continues pile of fuel, and with practically100% control of false air. This reduces the probability of uncontrolledgas explosions to a minimum. However, in order to break up eventualclogging of solid waste in the primary combustion chamber, the fuelsluice process can be delayed until a specified amount of the solid fuelinside the primary combustion chamber 1 is burnt such that asatisfactory gap is formed. Then the next bale of solid waste will fallonto the bridge/clogging and break it open. This is a very practicalsolution which can be performed during full operation of the plantwithin tolerable influences of the combustion process.

[0039] The lower part of the combustion chamber 1 is narrowed byinclining the longitudinal side walls 9 towards each other, thus givingthe lover part of the combustion chamber a truncated V-shape (see FIGS.3 and 4). A longitudinal, horizontal and rotable cylindrical ash sluice10 is located in the bottom of the combustion chamber 1 in a distanceabove the intersecting line formed by the planes of the inclined sidewalls 9. A longitudinal triangular member 12 is attached to the inclinedside wall 9 on each side of the cylindrical ash sluice 10. Thetriangular members 12 and the cylindrical ash sluice 10 will thusconstitute the bottom of the combustion chamber 1 and prevent ash or anyother solid matter from falling or sliding out of the combustionchamber. Solid incombustible remains (bottom ash) will therefore buildup in the area above the triangular members 12 and the ash sluice 10.The cylindrical ash sluice 10 is equipped with a number of grooves 11(see FIG. 5) spread out along its perimeter. When the ash sluicecylinder 10 is set into rotation, the grooves 11 will be filled withbottom ash when they are facing the combustion chamber and thereafteremptied when they are facing downwards. Thus the bottom ash will besluiced out and fall down into a vibrating longitudinal tray 13 locatedin a parallel distance underneath the ash sluice cylinder 10. In orderto ensure an absolute control with false air, the ash sluice 10 andvibrating tray 13 are encapsulated by a mantle 14 which are airtightattached to the lower part of the side walls of the primary combustionchamber 1.

[0040] The ash sluice is equipped with command logic (not shown) thatautomatically regulates its rotation. A thermocouple 15 is attached tothe transverse side wall in a distance above the ash sluice 10 (see FIG.4). The thermocouple continuously measures the temperature of the bottomash that builds up in the bottom of the combustion chamber 1 and feedsthe temperatures to the command logic of the ash sluice 10. The ashsluice cylinder 10 is driven by an electric motor (not shown) which isequipped with sensors for monitoring the rotation of the cylinder 10.When the temperature in the ash is cooled to 200° C., the command logicwill start the motor and set the ash sluice 10 into rotation in oneoptional direction. Since the old cooled bottom ash is removed andreplaced by fresher ash, the temperature of the bottom ash will increaseas long as the ash sluice is rotating. The command logic will stop therotation when the ash temperature reaches 300° C. In the case the ashsluice cylinder 10 is halted for instance by lumps of solid remains inthe bottom ash which are jammed between the sluice cylinder 10 and atriangular member 12, the command 20 logic will reverse the rotationaldirection of the ash sluice 10. Then the lump will often follow therotation of the cylinder 10 until it meets the other triangular member12 on the opposite side of the cylinder 10. If the lumps get jammed alsoon this side, the command logic will reverse the rotational directiononce more. This reciprocating rotation of the ash sluice 10 willcontinue as long as necessary. Most cases of lumps in the bottom ashthat are to big to be sluiced out, are remains of larger metallicobjects in the waste which have become brittle and fragile due to thehigh temperatures in the combustion zone. Thus the reciprocating motionof the ash sluice 10 will most often grind the lumps into smaller pieceswhich will be sluiced out of the combustion chamber. This is forinstance an effective way of dealing with the steel-cord remains whenburning car tyres. In some cases the metallic remains are so massivethat they resist the grinding motion of the ash sluice cylinder 10. Suchobjects must at be taken out of the chamber at regular intervals inorder to avoid filling up the combustion chamber with incombustiblematerial. The ash sluice cylinder 10 is therefore mounted resilientlysuch that it may be lowered either manually or automatically by thecommand logic in order to remove these solid objects in an efficient andfast manner without interrupting normal operation of the combustionchamber. The means for lowering (not shown) the ash sluice cylinder 10is of conventional type which is known to a skilled person and need nofurther description. It should be noted that when the ash sluicecylinder 10 is lowered, the control with false air is still maintainedsince all auxiliary means for lowering and rotating the cylinder islocated within the sealing mantle 14. Thus there will not be anypenetration of false air as long as the mantle 14 is closed. In thisway, the problem with false air has been practically eliminated with anenergy converting plant according to the invention, since both the fuelinlet and ash outlet are sealed off against the surrounding atmosphere.

[0041] The fresh air and recycled flue gas which is entered into thecombustion zone are inserted through one or more inlets 16 located onthe inclined longitudinal side walls 9 (see FIGS. 4-6). In the preferredembodiment, there are employed 8 rows with 12 inlets 16 on each sidewall 9, see FIG. 5. The flue gas is taken from the exhaust pipe 50 andis transported by pipe 55 which divides into one branch 56 for supplyingthe second combustion chamber 30 and one branch 57 for supplying theprimary combustion chamber 1 (see FIG. 2). The fresh air is pre-warmedby means of a heat exchanger 71 which exchanges the heat from the fluegas leaving the boiler 40, and transported through pipe 60 which dividesinto one branch 61 for supplying the secondary combustion chamber 30 andone branch 62 for supplying the primary combustion chamber 1. Branch 56and 61 are joined at junction 65 and branch 57 and 62 are joined atjunction 66. Further, branch 56 is equipped with valve 58, branch 57with valve 59, branch 61 with valve 63, and branch 62 with valve 64.This arrangement makes it possible to independently regulate the amountand ratio of fresh air and flue gas which are fed to both combustionchambers 1 and 30 by regulating/controlling the valves 58, 59, 63 and 64separately. After the pre-warmed fresh air and flue gas are mixed in thejunctions 65 and 66, they are sent via pipe 69 to the inlets 31 of thesecondary combustion chamber 30 and via pipe 70 to the inlets 16 of theprimary combustion chamber 1, respectively. Pipe 69 and 70 are equippedwith fans 67 and 68 for pressurising the gas-mixture before insertioninto the combustion chambers. Both fans 67,68 are equipped withregulating means (not shown) for regulating/controlling the insertionpressure of the gas-mixture, and they can be regulated independently ofeach other. In this way the ratio fresh air/flue gas can easily beregulated to any ratio from 0 to 100% fresh air, and the amount ofgas-mixture which is inserted into both combustion chambers 1 and 30 caneasily be regulated to any amount ranging from 0 to several thousandsNm³/hour.

[0042] Returning now to the primary combustion chamber 1. As mentioned,from FIG. 5 it can be seen that the inclined longitudinal side walls 9are equipped with eight rows each containing twelve inlets 16 in thepreferred embodiment of the invention. Referring to FIGS. 4-6, eachinlet 16 comprises an annular channel 17 with diameter of 32 mm and acoaxial lance 18 with internal diameter of 3 mm. This gives across-sectional area of the annular channel 17 which is approximately100 times larger than for the lance 18. Thus the pressure also fallswith a factor 100. The relatively large cross-sectional area of theannular channel 17 gives a low-pressure inlet stream with low flowvelocities, while the narrow lance 18 gives a highly pressurised gasstream with high flow velocities. Further, all annular channels 17 ineach row is connected to and extends into (through the inclined sidewall 9) one longitudinal hollow section 20 which runs horizontally onthe outside of the inclined longitudinal side wall 9. Each annularchannel is formed by a circular hole in the fire resistant lining 21 andthe lance 18 which is protruding in the centre of the hole. Thus, any asthat is fed into one hollow section 20 will run through the annularchannels 17 in one row. In addition, we have that two and two rows(hollow sections 20) on each side wall 9 are linked together such thateach double-row constitutes one regulation zone. Further, eachregulation zone are equipped with regulation means (not shown) forregulating/controlling the as flow and pressure in both hollow sections20 of each zone. The lances 18 of each row are connected to andextending into a hollow section 19 located on the outside the hollowsection 20 in the same manner as for the annular channels 17 (the lanceruns through the hollow section 20). The lances 18 are also organisedinto four regulation zones consisting of two neighbouring rows on eachside wall 9. Each regulation zone for the lances are also equipped withmeans (not shown) for regulating and controlling the gas stream andpressure inside the two hollow sections 19 of each zone. The ratio ofgas entering into the combustion chamber 1 through the annular channel17 and lance 18 can be regulated at any ratio from 0 to 100% through thelance 18 for each regulation zone independently. This arrangement givesthe opportunity to freely regulate the gas flow into the primarycombustion chamber in four independent zones (the regulation of the gasstream is symmetric above the vertical centre-plane in direction A givenin FIG. 3) at any flow rate and with any ratio of the gas-mixture from100% fresh air to 100% flue gas. For example, when starting up theincinerator, one should establish a controlled and stable combustionzone as soon as possible. This may be achieved by using a gas-mixturewhich consists of almost pure air and which is led through the lances 18in order to achieve a relatively violent (as stream in the solid wastein order to achieve a maximal forge effect. At the initiation of thecombustion process, the necessary heat energy is delivered by aconventional oil or gas burner 22 located at a distance above thethermocouple 15 on the lateral side wall 23 (see FIG. 4). The burner 22is only engaged at the initiation and is shut down under normaloperation of the plant. At a later stage when the combustion zone isnearly established and the temperatures have reached relatively highlevels, the forge effect should be reduced in order to prevent localoverheating. This can be achieved by inserting the gas through theannular channels and admix it with flue gas in order to reduce gas flowvelocities and diluting the oxygen content in the gas. These featurescombined with the feature of sluicing fuel in and ash out of thecombustion chamber give an excellent control with the oxygen flow in theentire combustion zone and practically eliminates the problem of falseair. In addition, the feature of admixing flue gas into the fresh airgives the opportunity to run the incinerator plant with highincineration capacities and relatively high bulk zone temperatures whileavoiding overheating any part of the combustion zone. Thus it ispossible to run the incineration plant at high capacities with lowemission levels of both CO and NO_(x), in contrast to prior artincinerators. Another advantage with the invention is that the capacityof the incinerator plant can quickly and easily be adjusted tovariations in the demand for energy by regulating the total amount ofsupplied flue gas and fresh air, and by regulating the relative amountsof gas which are inserted into the combustion chamber 1 through eachregulation zone. In this way, it becomes possible to maintain theoptimal temperature conditions in the combustion zone by adjusting theenergy production by regulating the “size” of the combustion zone.

[0043] The primary combustion chamber is equipped with at least one, butnormally at least two gas outlets. The first outlet 24 is located at adistance above the gas burner 22 on the vertical centre line of thelateral side wall 23, and the second outlet 25 is located on the samelateral side wall 23 in a relatively large distance above the firstoutlet 24 (see FIG. 3 or 4). The first outlet 4 has a relatively largediameter in order to lead out the combustion gases from the primarycombustion chamber 1 with small flow velocities. The small flowvelocities give a valuable contribution to the reduction of entrainedfly ash in the combustion gases. In addition the fly ash will also befiltered out of the combustion gas during its passing through the solidwaste that lies in between the combustion zone and the outlet 24. Theseeffects are sufficient to reduce the content of fly ash in thecombustion gases that leaves the primary combustion chamber toacceptable levels when the plant is fed with solid waste of low heatvalues, even though the outlet 24 is located in a relatively lowposition of the combustion chamber which means that the combustion gasesare filtered through relatively small amounts of solid waste. The uppergas outlet 25 is closed when the lower outlet 24 is employed duringincineration of waste with low heat values. The outlet 24 is connectedto pipe 26 which leads the combustion gases to the inlet 31 of thesecondary combustion chamber 30. In this case the temperature of thecombustion gases which leaves the primary combustion zone should be keptin the range of 700-800° C. This temperature is measured at the outlet24 and fed to the command logic (not shown) which performs theregulation of the gas flow in the primary combustion chamber 1.

[0044] In the case of burning waste with high heat values, there will bea much larger gas production in the primary combustion chamber, whichresults in much larger flow velocities of the combustion gases. Thisincreases the need for filtration capacity of entrained fly ash in thecombustion gases. In this case, the outlet 24 is closed by inserting adamper (not shown) and the upper outlet 25 is opened in order to forcethe combustion gases to run upwards through a major part of the primarycombustion chamber 1, and thereby filtrate the combustion gases in amuch larger portion of the solid waste in the chamber. The outlet 25 isconnected to pipe 27 which directs the combustion gases to the pipe 26.However, due to the prolonged filtration in a larger portion of thesolid waste, the combustion gases will be subject to a larger degree ofcooling by the solid waste. Thus it may be necessary to ignite thecombustion gases flowing in pipe 27 before they enter the secondarycombustion chamber 30. This can easily be performed by equipping thedamper which seals off outlet 24 with a small hole. Then a flame tonguewill protrude from the primary combustion chamber 1 into the pipe 26,and ignite the combustion gases as they pass on their way to the inlet31 of the secondary combustion chamber 30.

[0045] As mentioned, the hot combustion gases from the combustion zonein the primary combustion chamber 1 will pass through unburned solidwaste on their way out of the primary combustion chamber. Then thecombustion gases will give off heat to the solid waste and preheat it.The degree of preheating will vary from very high in the waste which isadjacent to the combustion zone to much lower for the waste further upin the combustion chamber. Thus the incineration process in the primarycombustion chamber is a mixture of combustion, pyrolysis andgasification.

[0046] The interior walls of the primary combustion chamber 1, withexception of the ash sluice cylinder 10, are covered by approximately 10cm of a heat and shock resistant material. It is preferred to employ amaterial which is sold under the name BorgCast 85 which has acomposition of 82-84% Al₂O₃, 10-12% SiO₂, and 1-2% Fe₂O₃.

[0047] Even though the invention has been described as an example of apreferred embodiment containing one lower outlet 24 placed in the sameheight as the upper inlets 16, the invention can of course be realisedby incinerators where there may be outlets with other diameters, atother heights, and with more than one outlet in use simultaneously. Itis envisaged that in the case of fuels with very high heat values, suchas for instance car tyres, the gas flow inside the plant becomes so highthat the secondary combustion chamber 30 does not have the necessarycapacity to complete the combustion of the gases leaving the primarycombustion chamber. In this case the plant may be operated with twosecondary combustion chambers attached horizontally side by side andthat the primary combustion chamber has two outlets 24 which also arelocated side by side, that these outlets 24 are closed with damperscontaining a small hole each, and that the combustion gas is taken outthrough outlet 25 which is branched to one supply line 26 for eachsecondary combustion chamber 30.

[0048] The Secondary Combustion Chamber

[0049] In the case of incinerating fuels with low heat values, it ispreferred to employ a secondary combustion chamber 30 as depicted inFIGS. 7 and 8. In this embodiment, the secondary chamber 30 is built inone piece with the pipe 26 which leads the combustion gases from theoutlet 24 of the primary combustion chamber 1. The interior of pipe 26is lined with a heat resistant material 28. The lining has a thicknessof approximately 10 cm and a composition of 35-39% Al₂O₃, 35-39% SiO₂,and 6-8% Fe₂O₃. The inlet for the combustion gases into the secondcombustion chamber is marked by flange 33 on FIG. 7, while the otherside of the pipe 26 is equipped with flange 29 which has the samedimensions as the flange 29A on outlet 24 on the primary combustionchamber (see FIG. 3). Thus the pipe 26 and secondary combustion chamberare attached to the primary combustion chamber 1 by bolting flange 29onto flange 29A.

[0050] The secondary combustion chamber is also equipped with inlets 31for the pressurised gas-mixture of fresh air and recycled flue gas. Thepreferred embodiment intended for fuels with low heat values, containsfour inlets 31 (see FIG. 7). Each of these are equipped with means (notshown) for regulating the gas flow, pressure and fresh air/flue gasratio in the same manner as each regulation zone of the gas inlets 16 ofthe primary combustion chamber 1. The secondary combustion chamber 30consists of a cylindrical combustion casing 32 which is tapered ornarrowed towards the inlet 33 for the combustion gases. Thus thecombustion chamber is expanded in order to slow down the combustiongases and thereby achieve longer mixing and combustion times in thechamber. Inside the combustion casing 32, there is located a secondperforated cylindrical body 34 (see FIG. 8) which is adapted to fit intothe combustion casing 32, but with a somewhat smaller diameter than theinner diameter of the combustion casing 32. The cylindrical body isequipped with outwardly protruding flanges 35 which also is adapted tofit within the combustion casing 32 with exactly the same outer diameteras the inner diameter of the casing 32. Thus the flanges 35 will formpartition walls which divides the annular space confined by thecombustion casing 32 and the perforated cylindrical body 34 into annularchannels. In this case there are three partition flanges 35 whichdivides the annular space into four chambers, one for each gas inlet 31.Thus, the pressurised fresh air and flue gas mixture which is sentthrough inlet 31 will enter into the annular chamber confined by thepartition flanges 35, combustion casing 32 and the perforatedcylindrical body 34, and from there flow through the holes 36 into tubes37 which leads the gas through the lining 28 which covers the interiorof the cylindrical body 34 (the lining is not included in the drawing)the interior of the cylindrical body 34 where they are mixed with thehot combustion gases. In this way it is achieved an even and finelydivided mixing, of the combustion gases and the oxygen containinggas-mixture in four separately regulated zones. This gives excellentcontrol with the combustion and temperature conditions inside thesecondary combustion chamber. The temperature inside the chamber shouldbe kept at approximately 1050° C. It is important to avoid highertemperatures in order to prevent formation of NO_(x).

[0051] A gas cyclone is attached to flange 38 at the outlet of thesecondary combustion chamber in order to provide a turbulent mixing ofthe combustion gases and oxygen containing gases in order to facilitateand complete the combustion process. The cyclone will also help reducingthe content of fly ash and other entrained solid particles in the gasflow. The cyclone is of conventional type which is well known for askilled person, and need no further description.

[0052] In the case of incinerating fuels with high heat values, it ispreferred to employ a second embodiment of the secondary combustionchamber as depicted in FIG. 9. In this case the combustion gas is takenout from the primary combustion chamber by outlet 25 and transported bypipe 27 down to pipe 26 on the outside of the closed outlet 24. Outlet24 is closed by a damper 39 which is equipped with a small hole in thelower part, from which a flame tongue 39A protrudes into pipe 26. Thesecondary combustion chamber 30 is attached to pipe 26, and consist inthis case of a cylindrical combustion casing 32 which is tapered towardsthe pipe 26. In this case there is no internal cylindrical body, insteadthe inlets 31 consist of perforated cylinders 31 which runs across theinterior of the combustion casing 32. From FIG. 8 we see that in thepreferred embodiment there are five inlets 31, the first is placed inthe pipe 26 and supplies the combustion gases which enters from pipe 27with the oxygen containing gas-mixture supplied from pipe 69 before thegas mixture is ignited by the flame tongue 39A. Then the gases passesthrough four inlet cylinders 31 which are aligned on top of each otherand receives additional supplies of the oxygen containing gas-mixture.As with the first preferred embodiment, this embodiment does alsoprovide means (not shown) for separate regulation of the gas-mixturecomposition and pressure for each inlet 31. There is also in this caseattached a gas cyclone at the outlet of the combustion chamber, but inthis case the gas stream velocities are sufficiently high to giveturbulent mixing of the combustion gas and the supplied gas-mixture alsoin the secondary combustion chamber. The temperatures in the combustionzone should also in this embodiment be kept at approximately 1050° C.

[0053] The regulation of the secondary combustion zone are performed bycommand logic (not shown) which regulates all inlet zones 31. Thecommand logic are continuously fed with the temperature, oxygen contentand total amount of the gas which leaves the gas cyclone, and employsthe information to regulate the temperature of the flue gas to 1050° C.and a oxygen content of 6%.

[0054] Auxiliary Equipment

[0055] The combustion gases will be turned into hot flue gases duringthe stay in the as cyclone. From the gas cyclone the flue gases will besent to a boiler 40 for transferring their heat energy to another heatcarrier (see FIG. 2). Thereafter, the flue gases are transported to agas filter 43 for additional reduction of fly ash and other pollutantsin the flue gas before they are discharged as exhaust gas. Both theboiler 40 and gas filter are equipped with by-pass pipes for the fluegas in order to provide the opportunity to shut-down the boiler and/orfilter during operation of the combustion chambers. The gas flow throughthe plant are governed by the fans for pressurising the inlets to bothcombustion chambers and by the fan 47 located in the exhaust pipe 50.The latter fan 47 ensures a good draft through the plant by providing aslight suction by lowering the gas pressure. All components of thisauxiliary equipment are conventional and well known to a skilled person,and need no further description.

EXAMPLE 1

[0056] The preferred embodiment of the invention will now be furtherillustrated by providing an example of incineration of ordinarymunicipal waste which is classified in Norway as class C. The waste isconsidered as a fuel with low heat values. Thus, it is the firstpreferred embodiment of the secondary combustion chamber which isemployed and which is attached to gas outlet 24 of the primarycombustion chamber. The upper gas outlet 25 is closed.

[0057] The municipal waste is compacted into large bales ofapproximately 1 m³ volume and then wrapped in PE-foil which are sluicedinto the top of the primary combustion chamber through sluice 5 withsuch a frequency that the primary combustion chamber is at any timefilled with solid waste. This is a cost-effective and very simplepre-treatment of the waste compared to the pre-treatments required byconventional incinerators. When the incineration process has beenestablished with a stable combustion zone, the gas-mixture which is ledinto the primary combustion chamber will be inserted through the annularchannels 17 of the inlets 16, and the oxygen content in the gas-mixturewill be held at approximately 10%. This concentration will result in anoxygen deficit in the combustion zone. The temperature in the combustiongases that leaves the primary combustion chamber is kept in the range of700-800° C., and the gas pressure inside the primary combustion chamberis kept at approximately 80 Pa below the surrounding atmosphericpressure. The oxygen content in the gas mixture which is led into thesecondary combustion chamber 30, through inlets 31, is regulated suchthat the total gas flow is approximately 2600 Nm³/MWh, has a temperatureof approx. 1050° C., and an oxygen content of approx. 6%. The pressurewithin the secondary combustion chamber is kept at approx. 30 Pa belowthe pressure in the primary combustion chamber. In order to ensure thatthe dioxin and furane emissions are kept at extremely low levels, thereis a possibility of adding an adsorbent to the flue as immediately afterit leaves the boiler 40 and enters into the filter 43. These featuresare not shown figures or discussed in the previous discussion, since themethod and means for performing this also are conventional and wellknown to a skilled person. A preferred adsorbent is a mixture of 80%lime and 20% activated carbon, and is supplied in an amount ofapproximately 3.5 kg per tonne fuel.

[0058] With the above parameters, the incineration plant was tested bythe Norwegian classification and verification firm, Det Norske Veritas.The energy production was approx. 2.2 MW. The content of fly ash andother pollutants in the flue gas leaving the plant was measured and isgiven in Table 1 along with the official emission limits for eachconstituent. The official emission limits are given for both thepresently valid limits for existing incineration plants and the futurelimits as proposed in a EU draft “Draft Proposal for a Council Directiveon the Incineration of Waste” dated Jun. 1, 1999.

[0059] From Table 1 it can be seen that the preferred embodiment of theinvention achieves emission values which are very comfortably below mostofficial limits valid for present incinerators, by a factor of at least10 below the limits. Even most of the future EU limits, which areconsidered to be very strict, will pose no problem with the possibleexception of NO_(x), where the value was just below the limit. All otherparameters are very comfortably below the future limitations as well.TABLE 1 Measured emission when incinerating municipal waste of Norwegiangrade C. Official emission limits Compound Results Present Future EUDust 3 30 10 Hg 0.001 0.1 0.05 Cd, Tl 0.004 0.05 Sb, As, Pb, Cr, Co, Cu,Mn, Ni, V 0.03 0.5 Cd 0.001 0.1 Pb, Cr, Cu, Mn 0.03 5 Ni, As 0.002 1 HCl5 50 10 HF <0.1 2 1 SO₂ 1 300 50 NH₃ 2 — — NO_(x) in form of NO₂ 170 —200 CO 1 — 50 TOC 1 20 10 Dioxins and furanes 0.0001 2 0.1

[0060] The plant has recently been modified such that also theNO_(x)-concentration in the flue gas leaving the gas cyclone is measuredalong with the oxygen concentration, temperature and flow velocity, andis fed to the command logic that regulates the inlets 31 of thesecondary combustion chamber 30. The command logic is given liberty tovary the oxygen concentration within the range of 4 to 8%. All otherparameters are left unaltered. With this modification, test runs haveshown that the NO_(x)-emissions are typically about 100 mg/Nm³ v/11% O₂,but has reached levels down to 50 mg/Nm³ v/11% O₂. The other pollutantspresented in Table 1 were not affected by this modification.

[0061] It should also be noted that if the flue gases are emittedwithout treatment with the adsorbent, the emission levels of dioxins andfuranes will be in the order of 0.15-0.16 ng/Nm³ v/11% O₂, which arewell below the present emission limits. Thus the present invention canpresently be employed without this feature.

EXAMPLE 2

[0062] In order to make the preferred embodiment of the invention asgiven above suited for handling toxic or any other form of special wastewhere the ash should be given a separate treatment than the ordinary ashfrom municipal waste, it is envisioned to include a pyrolysis chamberlocated in the flue gas stream exiting the second combustion chamber 30.There the flue gases will have a temperature of 1000-1200° C. which issufficiently high to decompose most organic and many inorganiccompounds. The pyrolysis chamber and design of the flue gas pipe 41containing the pyrolysis chamber is conventional and well known for askilled person and need therefore no further description.

[0063] A separate pyrolysis chamber makes is possible to sort outspecial waste from the bulk waste stream and decompose it in thepyrolysis chamber, such that the ash from the special waste can beseparated from the ash of the bulk part of the waste and thus avoid thatthe bulk volume of ash must be treated as special waste. This isbeneficial for cases where the special waste is toxic, for cremation ofpets or other applications where the ash must be traceable etc.

[0064] The vapours and gases from the pyrolysis chamber may subsequentlybe led to the primary combustion chamber and thus enter the main flow ofcombustion gases.

1. Method for converting by incineration the energy content in solidwaste to other energy carriers, where the incinerator comprises aprimary and at least one additional combustion chamber in which theprimary combustion chamber incinerates the solid waste while the atleast one additional combustion chamber finishes the combustion processby combusting the combustion gases exiting the first combustion chamber,characterised in that the oxygen flow in the primary and the at leastone additional combustion chambers are strictly controlled by separatelyregulating the flow of fresh air into each combustion chamber in atleast one separately regulated zone and by ensuring that the entirecombustion chambers are gas tight towards the surrounding atmosphere inorder to eliminate penetration of false air into the chambers, that thetemperatures in the primary and the at least one additional combustionchamber are strictly controlled, in addition'to the regulation of theoxygen flow, by admixing a regulated amount of recycled flue gas withthe fresh air which is being led into each of the chambers in each ofthe at least one separately regulated zones, and that the gases whichleave the combustion zone in the primary combustion chamber are ledthrough at least a portion of the primary combustion chamber's contentof solid waste before the gases exit the primary combustion chamber. 2.Method according to claim 1, characterised in that there is employed aprimary 1 and a secondary 30 combustion chamber, and that the regulationof the amount oxygen and the degree of admixture with recycled flue gasis performed in at least two independent inlets 16 or 31, or in at leasttwo independent groups of inlets 16 or 31 of the primary combustionchamber 1 and the secondary combustion chamber 30, respectively. 3.Method according to claim 2, characterised in that the regulation of theamount oxygen and the degree of admixture with recycled flue gas isperformed in four independent groups of inlets 16 or 31 of the primarycombustion chamber 1 and the secondary combustion chamber 30,respectively.
 4. Method according to claims 1-3, characterised in thatthe primary combustion chamber is fuelled with municipal solid wastewhich is compacted and wrapped in a plastic-foil to form odour-lessbales.
 5. Method according to claims 1-3, characterised in that theprimary combustion chamber is fuelled with untreated municipal solidwaste.
 6. Method according to claims 2-5, characterised in that when astable combustion zone in the primary combustion chamber 1 is achievedwhen burning wastes with low heat values, that the admixture and amountof the fresh air and recycled flue gas which is led into the primarycombustion chamber 1 is regulated to achieve an average concentration of10 vol % oxygen of the admixed inlet gases and a temperature in therange of 700 to 800° C. of the combustion gases which leave the primarycombustion chamber, and that the admixture and amount of fresh air andrecycled flue gas that is led into the secondary combustion chamber 30is regulated to gain an average surplus of oxygen of 6 vol %, atemperature of 1050° C., and a total gas flow of approx. 2600 Nm³/MWh ofthe flue gases which leaves the secondary combustion chamber.
 7. Methodaccording to claim 5, characterised in that the concentration of NO_(x)in the flue gas leaving the second combustion chamber 30 is monitored,and that the admixture and amount of fresh air and recycled flue gasthat is inserted into the secondary combustion chamber 30 isadditionally regulated by allowing the average surplus of oxygen in theflue gases which leaves the secondary combustion chamber to vary in therange from 4 to 8 vol % while keeping the temperature and total gas flowas in claim 5 with the aim to minimise the content of NO_(x) in the fluegas.
 8. Method according to claims 2-7, characterised in that thesecondary combustion chamber 30 is equipped with at least one gascyclone in order to turbulently mix the combustion gases with theinjected gas-mixture of recycled flue gas and fresh air and therebyachieve a complete combustion of the combustion gases.
 9. Methodaccording to claims 4-7, characterised in that the solid waste in theform of bales 80 is sluiced 35 in an air-tight manner into the primarycombustion chamber 1 by a sluice 5, and that the bottom ash is sluicedout of the primary combustion chamber through a sluice 10 which isencapsulated and sealed off by a mantle
 14. 10. Method according toclaims 1-9, characterised in that the vapours and gases from thepyrolysis chamber may subsequently be led to the primary combustionchamber and thus enter the main flow of combustion gases.
 11. Device forconverting by incineration the energy of solid waste to other energycarriers, where the device comprises at primary combustion chamberconnected to at least one additional combustion chamber, at least onecyclone, a unit for transferring the heat energy of the flue gases toanother heat carrier, a gas filter, a transport system for supplying andadmixing fresh air and recycled flue gas to combustion chambers,characterised in that the primary combustion chamber 1 is designed as avertical shaft with a rectangular cross-section and which is narrowed byinclining the lower part of the longitudinal side walls 9 towards eachother to give the lower part of the shaft a truncated V-shape, that theupper part of the shaft constitutes an air-tight sluice 5 for sluicingin the fuel in form of bales 80 of compacted solid waste, that thetruncated V-shape of the inclined longitudinal side walls 9 ends in anash sluice 10 for removal off bottom ash, that the ash sluice 10 issealed off toward the surrounding atmosphere by an air-tight mantle 14connected to the vertical shaft, that each of the inclined longitudinalside walls 9 are equipped with at least one inlet or interconnectedgroups of inlets 16 for insertion of the admixed fresh air and recycledflue gas mixture, and that at least one lateral side wall 23 of thevertical shaft is equipped with at least one outlet 24 or 25 for thecombustion gases that forms in the primary combustion chamber, that atthe at least one inlet or interconnected group of inlets 16 is equippedwith means for separately regulating the total gas flow and degree ofadmixture of fresh air and recycled flue gas through each inlet orinterconnected group of inlets, that at least one outlet 24 is connectedto an additional combustion chamber 30, that the at least one additionalcombustion chamber 30 is equipped with at least one inlet 31 forinjection of the admixed fresh air and recycled flue gas mixture, andthat each of the at least one inlet 31 is equipped with means forseparately-regulating the total gas flow and degree of admixture offresh air and recycled flue gas.
 12. Device according to claim 11,characterised in that when the incineration is fuelled by solid wastewith low heat values, there is employed one additional combustionchamber 30 which is attached directly to one outlet 24 of the primarycombustion chamber, and that the secondary combustion chamber comprisesa cylindrical combustion casing 32 and an adapted perforated cylindricalbody 34 which is inserted into the casing 32, and which equipped with atleast one outwardly protruding flange 35 such that the cylindrical body34 and casing 32 forms annular channels which is connected to the inlets31.
 13. Device according to claim 11, characterised in that when theincineration is fuelled by solid waste with high heat values, in thatthere is employed an additional combustion chamber 30 which is connectedto the outlet 24 through a pipe 26, that the outlet 24 is sealed by adamper 39 which is equipped with a small hole such that a flame tongueis protruding into the pipe 26, that the combustion gases are led fromthe primary chamber through outlet 25 in the upper part of the primarycombustion chamber and into pipe 26, and that the secondary combustionchamber 30 comprises a cylindrical casing 32 which is equipped with atleast one transverse running perforated cylinder which constitutes theinlet
 31. 14. Device according to claim 12, characterised in that thereis employed more than one secondary combustion chambers which each areconnected to an outlet 24 via a pipe 26, and that all pipes 26 areconnected to the outlet
 25. 15. Device according to claims 11-13,characterised in that the ash sluice 10 is shaped as a horizontallylongitudinal cylinder located in-between a triangular longitudinalmember 12 at the lower end of each of the inclined side walls 9., andthat the cylinder is equipped with at least one groove 11 such that thebottom ash is sluiced out when the cylinder 10 is rotated.
 16. Deviceaccording to claims 11-13, characterised in that each active outlet fromthe primary combustion chamber is equipped with means for measuring thetemperature of the combustion gases exiting the primary combustionchamber, and that the outlet from each of the at least one additionalcombustion chamber is equipped with means for measuring the total gasflow, temperature, oxygen content, and NO_(x)-content of the flue gasexiting the at least one additional combustion chamber.
 17. Deviceaccording to claim 15, characterised in that the means for measuring thetemperature of the combustion gas exiting the primary combustion chamberis connected to means for regulating the admixture and gas flow of themixed fresh air and recycled flue gas which is inserted through the atleast one inlet 16, and that the means for measuring the temperature,gas flow, oxygen content and NO_(x)-content in the flue gas exiting thesecondary combustion chamber is connected to means for regulating theadmixture and gas flow of the mixed fresh air and recycled flue gaswhich is inserted through the at least one inlet
 31. 18. Deviceaccording to any of claims 11-17; characterised in that a pyrolysischamber for decomposing of special waste is locate din pipe 41 forleading flue gas exiting the second combustion chamber 30 to boiler 40.